3,78 Proceedings of the Royal Physical Society. 



Palfeoniscid^ and Platysomidse. One of his discoveries that 

 has excited attention and interest is that of Palceospondylus 

 Gunni, named after its finder, Mr Marcus Gunn, from the 

 Caithness flagstones at Achanarras. Dr Traquair suggests 

 that, from its large single nasal opening, surrounded by cirri 

 and other characters, it may be an ancient Marsipobranch. 

 If this is not its true systematic position, then it is quite 

 impossible to refer it to any other group of existing 

 Vertebrata. 



Dr Traquair has also described, from the collection of the 

 Geological Survey obtained by Messrs Macconochie and 

 Tait from the Ludlow and Downtonian rocks of Lanarkshire 

 and Ayrshire, a suite of Fishes till then unknown to science, 

 with the exception of the genus Thelodus, the hollow scales 

 of which, mistaken for teeth by Agassiz, had been known to 

 occur in great numbers in the Ludlow " Bone-bed " and in 

 the Upper Silurian rocks of the Baltic. An entire specimen 

 of a problematical fish, from the Lower Old Eed Sandstone 

 of Forfarshire, had been in 1870 imperfectly described by 

 Powrie under the name of Gephalopterus Pagei, and this 

 was found by Dr Traquair to belong to Thelodus, and 

 re-described and figured by him as Th. Pagei. From the 

 Geological Survey collection he described two species of 

 Thelodus. He instituted the genus Lanarkia to contain 

 three species of similar form to Thelodus^ but having hollow 

 spines instead of scales, and placed both genera in the 

 family of the Coelolepidae. For a similarly shaped form, 

 with a strong resemblance to Cephalaspis, and having eye 

 orbits similarly placed, but in which the separate ossicles 

 which cover the head-shield are not confluent, he made the 

 genus Ateleaspis, which is apparently intermediate between 

 the Coelolepidae and the Cephalaspidae. Birhenia elegans is 

 the name of a shapely fish-like form, with the body and 

 tail and back fin reminding us of those of Cephalaspis, and 

 a row of hooked ridge scales along its central margin, but 

 which has no head- shield, and in which the head is covered 

 with small scutes. Lasanius prohlematicus and L. armatus 

 are regarded as nearly allied to Birkenia, having a row 

 of hooked ventral ridge scales, but with no further osseous 



